The invention relates to a multi-channel magnetic head having a head face which extends in a first direction in which a record carrier is relatively movable with respect to said magnetic head, and in a second direction transverse to the first direction, said magnetic head having a structure of layers which, viewed in the first direction, are situated one on top of the other and extend substantially in the second direction and in a third direction transverse to the first and the second direction, in which structure, viewed in the second direction, adjacent magnetoresistive sensors are distinguishable, each comprising a magnetoresistive measuring element, a first magnetic element and a second magnetic element, and in which, viewed in the first direction, the magnetic elements are situated opposite each other, at least the first magnetic element of said elements extending as far as the head face.
A multi-channel magnetic head of this type is known from EP-A 0 422 916. The known magnetic head comprises several magnetoresistive elements each forming part of a magnetic yoke which also comprises a shared flux guide and a magnetic substrate. During use, a measuring current for measuring resistance variations is passed through the magnetoresistive elements. To this end, each magnetoresistive element is provided with a current supply and a current return conductor which extend along the magnetic yoke. As a result of these conductors, the magnetoresistive elements in the known multi-channel head are situated at relatively large mutual distances so that only relatively small channel densities can be realized.
It is an object of the invention to provide a multi-channel magnetic head in which the channel density is independent of the current supply and current return conductors of the magnetoresistive measuring elements which are present.
The magnetic head according to the invention is characterized in that both magnetic elements of each of the at least two adjacent magnetoresistive sensors are electrically conducting, the measuring element being electrically arranged in series between the two magnetic elements for passing a measuring current through the measuring element substantially in the third direction, both magnetic elements having an electric connection face. By having the same elements perform both magnetical and electrical functions, the separate sensors may be given a compact shape. Particularly the width, viewed in the second direction, of the sensors can be completely determined by the desired channel width. Consequently, magnetoresistive measuring elements may be provided very close together, which results in large channel densities. An additional, but important advantage is that electrostatic discharge problems can be prevented because insulating oxide layers between the measuring elements and the magnetic elements and between the magnetic elements themselves are not necessary, across which layers electric charge might build up and discharge. The absence of insulating oxide layers between measuring elements and magnetic elements also ensures a favorable efficiency. A further advantage is that the measuring elements are electrically connected to the magnetic elements so that a possible flashover from a measuring element to a magnetic element is prevented.
An anisotropic magnetoresistive (AMR) element or a giant magnetoresistive (GMR) element may be used as a measuring element. An AMR element may be, for example a layer of an NiFe alloy with or without equipotential strips which are generally referred to as barberpole stripes. A favorable embodiment of the AMR element is a laminated magnetoresistive element of the type as shown in U.S. Pat. No. 4,686,472 (herein incorporated by reference). A favorable GMR element is described in, for example WO-A to which U.S. Pat. No. 5,600,297 corresponds, herein incorporated by reference).
An AMR element may be biased by using a DC current-conveying conductor preferably placed between the magnetic elements. A GMR element of, for example the spin valve type has the advantage that biasing is not absolutely required.
The multi-channel magnetic head according to the invention may be manufactured by means of a known thin-film technology, in which the magnetic elements are thin films formed from, for example, NiFe, CoNbZr or FeNbSixe2x80x94N. One of the magnetic elements may be alternatively constituted by an electrically conducting, magnetically permeable substrate.
In principle, the multi-channel magnetic head according to the invention is suitable for any application in which narrow, closely spaced tracks must be scanned. Examples are tape streamers, digital video recorders, hard disk drives and multimedia recorders for video/data storage. Particularly in linear recorders, a large number of tracks is desired so as to achieve a high data rate due to the relatively low speed of the information medium with respect to the head. This speed is considerably higher in helical-scan recorders.
An embodiment of the multi-channel magnetic head according to the invention is characterized in that, of each of at least two adjacent sensors, an electrically conducting third magnetic element extending as far as the head face is present, which third element, together with the second magnetic element not extending as far as the head face, bounds a non-conducting space which is bridged by the magnetoresistive element which, beside said space, is in electric contact with the second and the third magnetic element, while an electrically conducting gap layer electrically interconnecting the first magnetic element and the third magnetic element extends proximate to the head face. In this embodiment, which is of the yoke type, the magnetic elements are used for electrically conducting measuring currents and for the supply and return of magnetic flux coming from the medium to be scanned. The magnetic elements are therefore current-conveying flux guides during operation. The gap layer is preferably a metal layer of, for example Ag or Cu.
It is to be noted that a single-channel magnetic head of the yoke type, in which electrically conducting yoke parts are used, is known from U.S. Pat. No. 5,493,467. The known magnetic head is provided with one spin-valve magnetoresistive element incorporated in a magnetic yoke. Two yoke parts of this yoke are electrically interconnected on a head face of the magnetic head by means of an electrically conducting gap layer. One of the yoke parts has an interruption which is electrically and magnetically bridged by the magnetoresistive element. In an area spaced apart from the head face, the yoke parts are provided with electrically conducting layers which are oriented transversely to the yoke parts and terminate in connection faces present beside the yoke parts.
An embodiment of the multi-channel magnetic head according to the invention is characterized in that the magnetoresistive measuring element of each of at least two adjacent sensors adjoins the head face, while a part of the measuring element situated proximate to the head face is electrically connected to one of the two magnetic elements, being the first or the second magnetic element, and a part of the measuring element spaced apart from the head face is electrically connected to the other magnetic element of the two elements. In this embodiment, which is of the shielded type, the magnetic elements are used for electrically conducting measuring currents and for magnetically shielding the measuring elements. The magnetic elements are therefore current-conveying shields during operation. The electric connections between the measuring elements and the magnetic elements may be constituted by mutual contact faces or by electrically conducting intermediate layers which are present, such as metal layers of, for example gold or copper. When AMR elements are used, it may be favorable, in connection with biasing, to form the electrically conducting intermediate layers spaced apart from the head face from an electrically conducting anti-ferromagnetic material such as FeMn.
It is to be noted that a single-channel magnetic head having a shielded magnetoresistive element is known from EP-A 0 457 278. The magnetic head has a lower and an upper shielding magnetic layer, between which layers the magnetoresistive element extends. The magnetoresistive element is provided with electrodes at a head face of the magnetic head and at an edge spaced apart from the head face, while the electrode on the head face is electrically connected via a conducting layer to the upper shielding layer which is grounded via an electric wire, and the electrode spaced apart from the head face is electrically connected to the input of an amplifier unit via an electric wire.
An embodiment of the magnetic head according to the invention is characterized in that the connection face of the first magnetic element and the connection face of the second magnetic element of each of at least two adjacent sensors are situated within a zone having an extensiveness in the second direction which is determined by the extensiveness in the second direction of the relevant magnetic element. Multi-channel heads having large channel densities can be technologically realized in a simple manner by this practical measure. A further measure, in which the connection face of the first magnetic element and the connection face of the second magnetic element of each of at least two adjacent sensors are situated on the relevant magnetic element, also leads to a reduction of the number of technology steps. For connecting the multi-channel head in a scanning device, it is favorable if, viewed in the third direction, the connection face of the first magnetic element of each of at least two adjacent sensors is offset with respect to the connection face of the second magnetic element.
An embodiment of the magnetic head according to the invention is characterized in that at least two adjacent sensors have a common electrically conducting magnetic element constituting the first magnetic element in each sensor. The common magnetic element which is present renders a favorable shape-anisotropy possible, inhibiting the creation and possible displacement of domain walls in the first magnetic elements, which is favorable for the signal-to-noise ratio. If third magnetic elements are present, they may be formed as common elements, with or without the presence of the above-mentioned common magnetic element.
An embodiment of the magnetic head according to the invention is characterized in that at least the first magnetic element of each of at least two adjacent sensors has a relative magnetic permeability which is larger in the third direction than in the second direction. The magnetic anisotropy which is present ensures an accurately defined scanning width. The measure formulated here has a favorable effect on magnetic heads with sensors provided with individual magnetic elements which are spaced apart at some distance, and on magnetic heads in which a common magnetic element is used. In the latter case, the anisotropy ensures the desired channel separations. The manufacture of such magnetic heads has technological advantages, particularly in that fewer and less complicated manufacturing steps are required for which, in principle, the common magnetic element requires no structuring.
It has been found that as the permeability in the third direction is larger with respect to the permeability in the second direction, the sharpness of the channel separation increases so that larger channel densities are possible. A suitable value appears to be given if the relative magnetic permeability in the third direction is at least a factor of 25 larger than the relative magnetic permeability in the second direction.
The invention also relates to a device for scanning a record carrier such as a magnetic tape or disc, which device includes the multi-channel magnetic head according to the invention.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.